My credit and debit cards do not have my signature on the back of them. Instead, I wrote "SEE ID" where the signature should go. The signature on the back of the card is pretty useless, so I'd rather have a retailer ask to see my ID when I use a card. Most of the time, the retailer ignores it anyway. Sometimes, they ask for my ID, but a lot of those times, it's just the store policy to do that anyway. I know that technically, the card is not valid unless signed -- it says so right on the card. I've never had a problem with it.

Today, I went to the post office. After ringing me up and looking at my card, the teller informed me that he couldn't accept the card unless it was signed. No big deal, I've heard about that happening to people who write "SEE ID" on their cards. You can fix the problem by just signing the card on the spot. I didn't have a pen on me (I need to get back in the habit of keeping a pen on me) so I asked to borrow his. He gave it to me. I made some scribbles that was not my signature on the card and handed it back to him. He was cool with that and rang up the transaction. When he gave me my card back, the ink of my scribbles was still wet, so I just wiped the scribbles off.

How many ways was this whole transaction wrong?

My card wasn't signed to begin with. According to the card, that means it's invalid.

When the teller refused to accept my invalid card (good for him, I guess), he allowed me to sign it in front of him and accepted the card.

I "signed" the card with scribbles that looked nothing like my signature.

My scribbles were never compared with the signature on the credit card receipt that I did sign with my real signature.

When it was all done, I just erased the scribbled "signature" off my card.

What is the point of requiring a signature of the back of the card in order for the card to be valid?